Under the circumstances of a recent rise in environmental problems, attention has been paid to hydroelectric power generation, wind power generation, and photovoltaic power generation as clean energy. Among these, photovoltaic power generation has seen a remarkable improvement in performance such as the power generation efficiency of solar cell modules, and an ongoing decrease in price, and national and local governments have worked on projects to promote the introduction of residential photovoltaic power generation systems. Thus, in recent years, the spread of photovoltaic power generation systems has advanced considerably.
By photovoltaic power generation, solar light energy is converted directly to electric energy using a semiconductor (solar cell element), such as a silicon cell. The performance of the solar cell element utilized there is deteriorated by contacting the outside air. Consequently, the solar cell element is sandwiched by an encapsulant or a protective film for providing buffering and prevention of contamination with a foreign substance or penetration of moisture.
As a sheet for this solar cell encapsulant, a crosslinking product of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% to 33% by weight is generally used in view of transparency, flexibility, and adhesiveness to various members constituting a solar cell module, in view of durability to maintain these transparency, flexibility and adhesiveness for a long time, in view of processability into sheets, and in view of ease of handling in the form of a sheet during the manufacture of solar cell modules (see, for example, Patent Document 1).
Furthermore, incorporation of a silane coupling agent to improve the adhesiveness of a sheet for solar cell encapsulant which is formed of an ethylene-vinyl acetate copolymer is known (see, for example, Patent Document 2).    Patent Document 1: Japanese Examined Patent Application Publication (JP-B) No. 62-14111    Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2006-36875